Changes needed for ACP, ThresholdMessageKit work in `nucypher-core` #460

Job	Run time
check	3m 52s
wasm-test (1.67, wasm32-unknown-unknown)	9m 58s
wasm-test (stable, wasm32-unknown-unknown)	5m 45s
python-test (stable, wasm32-unknown-unknown, 3.10)	2m 3s
yarn-test (stable, wasm32-unknown-unknown)	4m 51s
test (x86_64-unknown-linux-gnu, 1.67)	7m 33s
test (x86_64-unknown-linux-gnu, stable)	5m 0s
codecov	9m 14s
benchmark	0s
	48m 16s

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